Packaging substrates of electronic components and the like are fabricated by laminating wiring layers and insulating layers on a core substrate to form a large wiring substrate provided with a number of wiring patterns, followed by dicing the wiring substrate into pieces to produce the packaging substrates each having a predetermined size. In the fabrication of wiring substrates, two or more resin layers (insulating layers) and wiring layers are laminated on a core substrate, the layers each having a linear expansion coefficient different from that of the core substrate. With this configuration, the difference in the linear expansion coefficient increases the difference in expansion between the resin layers, the wiring layers and the core substrate if there is a change in temperature. In such a case, it is known that stress is applied to an outer peripheral portion of the core substrate.
Core substrates used for recent packaging substrates include ones made of materials that are brittle, although they have good electrical properties. When a core substrate is made of such brittle materials with which the core substrate is likely to be broken, minute cracks may develop at the cut surfaces of the core substrate due to the impact generated at the time of cutting the core substrate by dicing. Due to the minute cracks at the cut surfaces of the core substrate, internal stress accumulated in the core substrate due to temperature change is released from cracked portions due to temperature change immediately after dicing or during the subsequent process, which may result in extension of cracks in directions along which the core substrate splits. When such a core substrate is a glass substrate having a thickness of more than several tens of micrometers, and used in a laminate, the glass substrate is likely to split from the end surfaces.
Examples of a method of dicing a wiring substrate into pieces without developing such cracks include a method of forming a metal layer at a portion of the core substrate, corresponding to an outer peripheral portion of the packaging substrate, followed by etching away the metal layer that has been exposed after dicing the wiring substrate into pieces to create a trench constituted by the core substrate and an insulating layer. Provision of the trench can better prevent the outer peripheral portion of the core substrate from being stressed. Therefore, such a simple configuration can effectively better prevent breakage of the core substrates (see, for example, PTL 1).
This method, however, uses a dicing blade to cut the metal layer on the core substrate, and therefore cutting ability of the dicing blade may be decreased due to clogging of the dicing blade. In that case, cracks are more likely to occur at the cut surface of the core substrate. Therefore, the core substrate may be broken immediately after being diced into pieces in a dicing process.